Plants for a cold room

A cold room is not a cold climate. It is an ordinary room that nobody heats: a spare bedroom, a hallway, a porch, a conservatory or a landing, where a winter night takes the air down close to the temperature outside. What matters to a plant there is the lowest temperature the room reaches, and every entry in the journal records the point below which that plant is damaged. The entries on this page have a minimum of 10 degrees Celsius or lower.

That number is a floor and not a target. A plant listed at 10 will survive a room that touches 10 and has no margin there, while one listed at 5 or below has real room to spare. Read the figure on the entry, then put a thermometer that records the lowest reading where the plant will stand and check it after the coldest night, not after a mild afternoon. Cold means winter, which falls in December to February north of the equator and June to August south of it, so look at the room in its own cold weeks.

The mistake that kills them

Cold and wet together. A plant in a cold room is barely growing, so it uses almost no water, and the compost stays wet far longer than the log’s interval assumes. Cold wet compost in a dark room is the commonest way a houseplant dies in winter. In a heated room the watering interval may have doubled by midwinter, and a cold room dries more slowly again. Let the finger decide, never the calendar, and stop feeding while growth is stopped, because fertiliser given to a plant that is not growing only builds up in the compost as salt.

The second mistake is the pane. Leaves that touch cold glass overnight brown in patches, so keep foliage clear of the window, and keep the glass clean, because in winter every bit of light matters. The guide to watering houseplants in a southern winter covers the same slowing of the year from the southern side, and the guide to moving plants between seasons explains why the watering interval follows the light rather than the thermometer.

A cool room is not always a problem for the plant. A clivia, for one, is meant to spend its winter cool and barely watered, because that rest is what sets its flowers.

How the list was chosen

An entry is listed here when the minimum temperature recorded on it is 10 degrees Celsius or lower, when the plant can live indoors, and once the entry has been reviewed. The list leaves out the vegetables, fruit, herbs and annuals of the kitchen garden, which are summer crops with a shelf of their own. It is sorted with the easiest first, then by name.

Being able to stand the cold is not the same as liking it. Most of these plants grow little or nothing at the low end of their range, and all of them still need the light the entry asks for. Choose by the coldest night, then by the light, and water last.